1. Technical Field
This invention relates to a mobile apparatus for scrubbing gases, or stripping liquids, containing hazardous materials, and more particularly to such an apparatus for removing hazardous gases such as ethylene dichloride and hydrogen sulfide from enclosed storage tanks or other vessels.
2. Background Art
Petroleum products, particularly crude oil, are stored in tanks, many of which are very large, holding as much as 500,000 barrels of crude oil. Such tanks may exceed 250 feet in diameter. Crude oil stored in these tanks deposit sludges which accumulate on the bottom of the tanks, resulting in operational problems and diminished volumetric capacity. Several methods have been devised to simplify the cleaning of these tanks and the removal of accumulated sludges from the tanks. For example, such methods and equipment are described in U.S. Pat. Nos. 4,945,933, 4,817,653, 5,091,016 and 4,407,678. While each of these patents describes successful means for handling the sludges in various way, another problem has existed with respect to sour crude oil storage that is not addressed by any of the aforementioned art and, yet, creates an extremely hazardous situation for ultimate cleaning of storage tanks, requiring the entry of work people into the tanks.
An environmental concern has also developed in connection with soils contaminated with volatile hazardous gases, such a ethylene dichloride. Often the only solution for containment of the solids contaminated with ethylene dichloride in a benign manner is by using an enclosed storage tank as a holding vessel for such contaminated soils. As the soil lies in the tank, the volatile ethylene dichloride permeates the atmosphere within the tank, creating a dangerous situation of proportions equal to that of the hydrogen sulfide invasion of the contained atmosphere of a hydrocarbon storage tank.
Additionally, the entry of a worker into an atmosphere of ethylene dichloride requires care equal to that of the care required in an atmosphere invaded by hydrogen sulfide. Many attempts have been made to avoid the necessity of entry into such tanks which burdens the worker by the necessity of wearing heavy, hot and cumbersome equipment to the extent that efficiency is lost and dangerous, life threatening work situations occur, particularly in the enclosed tank atmosphere during hot periods, such as summer along the Texas and Louisiana Gulf Coast where many such tanks exist.
Ethylene dichloride poses a particularly troublesome problem since it is water soluble and leaches from surface soil into progressively deeper areas of soil and into lakes and streams and, accordingly, presents a threat to water supplies. Therefore, is must be removed. However, without adequate means of containment the removal and treatment becomes a complicated environmental problem. For example, when stored in closed containers, such as large storage tanks, the vapor pressure of ethylene dichloride increases at elevated temperatures and, in a relatively short time, the entire atmosphere within the storage tank is saturated with the hazardous gas mixture.
Because of continued governmental regulations, such as the Resource Conversion and Recovery Act (RCRA) and the Hazardous and Solid Waste Amendment of 1984 (HSWA), which establish comprehensive "cradle to grave" provisions to regulate hazardous materials, there is an increased need for the efficient removal of volatile compounds from solid materials and enclosed environments.
An effective method for removing hazardous gases from enclosed structures is described in copending application Ser. No. 08/084,619, now U.S. Pat. No. 5,634,962 also assigned to the Assignee of the present invention. The treatment method described in the copending application includes withdrawing hazardous, water soluble gases from a vessel and introducing the gases into a scrubbing zone while expanding the gases. Desirably, the described treatment method is carried out on-site, i.e., in proximity to the storage vessel or tank. However, on-site equipment takes up valuable space in usually already crowded physical plants at which large storage tanks are typically placed. Also, on-site equipment is expensive to construct, maintain and operate if not required or used on a substantially continuous, or at least frequent, basis.
The present invention is directed to overcoming the problems set forth above. It is desirable to have an apparatus for effectively removing undesirable, water soluble compounds from a gas, without requiring the entry of workers into a vessel in which the gas is contained. It is also desirable to have such an apparatus that is mobile, and can be moved from site-to-site, as needed, to remove contaminate materials from the enclosed environment of a storage tank. Furthermore, it is desirable to have a mobile apparatus capable of separating water soluble hazardous materials from a gaseous mixture enclosed within a storage tank, and then recirculating the cleaned gases to the tank to sweep additional hazardous materials from the tank.